Organic optoelectronic devices, including organic light emitting devices, organic phototransistors, organic photodetectors, and organic photovoltaic devices, are known in the art and are frequently used in connection with multi-device arrays.
For example, organic light emitting devices (“OLEDs”), including both polymer and small-molecule OLEDs, are potential candidates for a great variety of virtual- and direct-view type displays, such as lap-top computers, televisions, digital watches, telephones, pagers, cellular telephones, calculators and the like. Unlike inorganic semiconductor light emitting devices, organic light emitting devices are generally simple and are relatively easy and inexpensive to fabricate. Also, OLEDs readily lend themselves to applications requiring a wide variety of colors and to applications that concern large-area devices.
In general, two-dimensional OLED arrays for imaging applications are known in the art and typically include an OLED display area that contains a plurality of active pixels arranged in rows and columns. FIG. 1A is a simplified schematic representation (cross-sectional view) of an OLED structure of the prior art. The OLED structure shown includes a single active pixel 15 which includes an electrode region such as anode region 12, a light emitting region 14 over the anode region 12, and another electrode region such as cathode region 16 over the a light emitting region 14. The active pixel 15 is disposed on a substrate 10. With the aid of a sealing region 25, the cover 20 and the substrate 10 cooperate to restrict transmission of oxygen and water vapor from an outer environment to the active pixel 15.
Traditionally, light from the light emitting layer 14 was transmitted downward through the substrate 10. In such a “bottom-emitting” configuration, the substrate 10 and anode 12 are formed of transparent materials. The cathode 16 and cover 20, on the other hand, need not be transparent in this configuration.
Other OLED architectures are also known in the art, including “top-emitting” OLEDs and transparent OLEDs (or “TOLEDs”). For top-emitting OLEDs, light from the light emitting layer 14 is transmitted upward through cover 20. Hence, the substrate 10 can be formed of opaque material, while the cover 20 is transparent. In some top-emitting configurations, which are based on a design like that illustrated in FIG. 1A, a transparent material is used for the cathode 16, while the anode 12 need not be transparent. In other top-emitting configurations, the positions of the anode 12 and cathode 16 in FIG. 1A are switched as illustrated in FIG. 1B, such that a transparent anode 12 is used. In this embodiment, the cathode 16 can be opaque.
For TOLEDs, in which light is emitted in both up and down directions (that is, out of both the top and bottom of the device), the substrate 10, anode 12, cathode 16 and cover 20 are all transparent. The configuration used can be like that of FIG. 1A or that of FIG. 1B.
Unfortunately, certain OLED structure components, such as reactive metal cathode components, are susceptible to oxygen and moisture, which exist in the ambient atmosphere and can produce deleterious effects that can severely limit the lifetime of the devices. For example, moisture and oxygen are known to increase “dark spot areas” in connection with OLED structures.
As a result, a getter material is frequently applied inside the encapsulated region of the device to absorb any moisture and oxygen entering the device. However, due to the fashion in which the getter material is disposed inside the cover, if this device design were to be used in connection with a top-emitting or transparent OLED configuration, then the getter would obstruct the transmission of light to the outer environment.